The stuff of Mosaic : Stones

Stones are classified base on 2 criteria : how they are made, and what composes them.

Stones were formed a long time ago according to 3 different processes

1 - Born of fire : the Igneous Stones.

These are stones that were once very hot and liquid and cooled down underground. Their grains look like small flecks typically spread consistently throughout stone. They are hard (cannot be scratched by steel) and dense.

Granite is a typical igneous stone used in mosaic. 

Blue Granite

2 - Sedimentary Stones

These stones are formed through the compacting of grains or pieces of any kind of existing rock material. These existing rocks may have been weathered, transported, deposited and then cemented over millions of years by the movement of the earth’s tectonic plates. Sedimentary stones sometimes contain fossils or other distinct features formed at the time of deposition.

Limestones and Travertines are sedimentary stones used in mosaic.

Raw travertine

Gold Travertine

3 - Metamorphic Stone – “Changed in Structure”

They were formed at extremely high pressures and temperatures but did not melt like igneous stones did. The presence of swirls, linear patterns or banding is a key characteristic of metamorphic stones

Marble, Agates, and Slate are metamorphic stones used in mosaic. 

Raw agate

4 slates.

Marble.

2 . Mineral Composition of Stones

Stones basically made of 2 different stuffs  : Silicate (Silicium Oxyde SiO₂₎ and Calcium Carbonate (CaCO₃)

21 - Silicates

These stones are made mostly of quartz-like particles called silica. They are very hard, durable and generally acid resistant.

Granites, Flint and Slates are Silicates used in mosaic. 

22 - Calcium Carbonates 

The minerals in these stones were formed under pressure over millions of years from the bodies of tiny fossilized creatures. These stones are softer, less durable than silicates and acid sensitive.

Limestones, Marbles and Travertines are Calcium Carbonates used in mosaic.

 

 

 

Tesshu's Tiger - Travertine and Granite